The presnet invention relates to a fuel injection control apparatus for controlling a fuel injection valve for use of a gasoline engine, and more particularly to a fuel injection control apparatus which sets an opening timing of a fuel injection valve according to a driving condition of an engine and independently injects a specific amount of fuel into each of cylinders in the engine.
In general, there has been proposed such an independent fuel injection control apparatus for injecting fuel independently into each cylinder through a fuel injection valve provided in each intake manifold. The independent fuel injection control apparatus calculates an amount of fuel to be injected so that an air-fuel ratio may be adjusted to an optimum value according to driving conditions such as an engine RPM and an amount of air suctioned into the engine. Next, according to the calculated amount of fuel to be injected, the fuel injection valve is opened for an each cylinder at the timing when each piston within each cylinder is positioned at a predetermined crank angle. Thus, according to the previous independent fuel injection control apparatus, the fuel injection is controlled according to the driving conditions of a vehicle. However, the opening timing of the fuel injection valve is fixed regardless of the driving conditions.
In general, the time period from when an intake valve opens until when the injected fuel is completely suctioned into an engine combustion chamber is very short. This time period varies according to the driving conditions. Hence, if the intake valve opens for only a short time, the entire amount of the injected fuel is not completely suctioned into the cylinder according to the driving conditions of the engine. Further, when the suction speed of the mixture of an air and a fuel is low, the air cannot be satisfactorily mixed with the injected fuel. Particularly, when an engine speed is low, the suction speed of the mixture is low and therefore the mixing between the air and fuel is not thorough. The opening timing of the fuel injection valve is fixed, according to the prior fuel injection control apparatus, which impairs the stability of fuel combustion and the fuel consumption rate. This adversely affects the exhaust gas emission and the engine response during a transient time of the engine. Moreover, it is difficult to obtain the optimum opening timing of the fuel injection valve.